DocID023654 Rev 2

11/27

ST1S41

Functional description

The transfer function from FB to Vc (output of E/A) introduces the singularities (poles and

zeroes) to stabilize the loop. Figure 5 shows the small signal model of the error amplifier

with the internal compensation network.

Figure 5. Small signal model for the error amplifier

system stability and can be neglected.

Equation 9

Equation 10

Equation 11

whereas the zero is defined as:

Equation 12

considered as negligible. The error amplifier output resistance is 240 M

Ω so the relevant

singularities are:

Equation 13

Co

Ro

Cc

Rc

Cp

Vd

AM15062v1

G

()

G

EA0

1s

+

R

c

C

c

⋅⋅

()

⋅

s

2

R

0

C

0

C

p

+

() R

c

C

c

sR

0

C

c

⋅

R

0

C

0

C

p

+

() R

c

C

c

⋅

+

⋅

+

() 1

+

⋅

+

⋅⋅

⋅

⋅

---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

=

f

P LF

1

2

π R

0

C

c

⋅⋅

⋅

------------------------------------------

=

f

P HF

1

2

π R

c

C

0

C

p

+

()

⋅⋅

⋅

------------------------------------------------------------

=

f

Z

1

2

π R

c

C

c

⋅⋅

⋅

------------------------------------------

=

f

Z

11.6 kHz

f

PLF

3.4 Hz

=

=